Re: [OSPF] RtgDir QA review: draft-ietf-ospf-segment-routing-extensions-12

Peter Psenak <ppsenak@cisco.com> Thu, 04 May 2017 10:02 UTC

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Date: Thu, 04 May 2017 12:02:19 +0200
From: Peter Psenak <ppsenak@cisco.com>
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To: Stig Venaas <stig@venaas.com>, rtg-dir@ietf.org, ospf@ietf.org, ospf-chairs@ietf.org, draft-ietf-ospf-segment-routing-extensions.all@ietf.org
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Subject: Re: [OSPF] RtgDir QA review: draft-ietf-ospf-segment-routing-extensions-12
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Hi Stig,

a new version that includes your comments has been published.

https://www.ietf.org/internet-drafts/draft-ietf-ospf-segment-routing-extensions-13.txt

thanks,
Peter


On 03/05/17 17:18 , Peter Psenak wrote:
> Hi Stig,
>
> please see inline:
>
> On 27/04/17 00:08 , Stig Venaas wrote:
>> Hello,
>>
>> I have been selected as the Routing Directorate reviewer for this
>> draft. This is just an early QA review.
>>
>> The draft is in good shape, but I did find some minor issues and nits.
>> It is fairly readable, but it could be improved in a few places.
>>
>>
>> Minor issues:
>>
>> In 3.1:
>> The SR-Algorithm TLV is some places called a Sub-TLV. It might be
>> good to be consistent.
>
> fixed.
>
>>
>> This is not clear in 3.1:
>>     The SR-Algorithm Sub-TLV is optional. It MAY only be advertised once
>>     in the Router Information Opaque LSA.
>> Is this trying to say that it MUST NOT be advertised more than
>> once? With the current wording this is not obviously that strict.
>
> yes, I changed the text to: "It MUST only be advertised once in the
> Router Information Opaque LSA". Hope that is clear enough.
>
>
>>
>> I see some text regarding multiple SR-Algorithm sub-TLVs, but it also
>> looks like one can have multiple algorithms in one sub-TLV. At least
>> from the diagram.
>
> yes, multiple algorithms in the same SR-Algorithm TLV is fine.
>
>> But I don't see any discussion about this. Is it OK
>> to add multiple? When can it be done, what does it mean? What if
>> routers don't support the exact same set of algorithms?
>
> router advertise all algorithms it supports. Each router may support
> different set.
>
>>
>> The term "lowest flooding scope" is used a couple of places. I think I
>> know what it means, but it might be good to point it out. Also, I'm
>> used to seeing the term "smallest" rather than "lowest". I'm assuming
>> they mean the same.
>
> I changed all places to "narrowest flooding scope".
>
>>
>> In 3.2 there is this bullet point:
>>     The receiving router must adhere to the order in which the ranges
>>     are advertised when calculating a SID/label from a SID index.
>>
>> You probably should use MUST here.
>
> fixed.
>
>>
>> Section 4:
>> In section 4 there is a range for advertising a range of prefixes.
>> But it looks like it contains a single prefix length and it says
>> the length is the length of the prefix. While it says range size
>> is the number of prefixes. I don't understand from the text what
>> really prefix length and range size means and how this should be
>> used.
>
> 10.0.1.0/24 - 10.0.100.0/24 represents a range of 100 /24 prefixes, where:
>
> (starting) prefix - 10.0.1.0
> length of the prefix is 24
> range size is 100
>
>>
>> I understand this is IPv4 only since OSPFv2, but rather than just
>> saying IPv4 is 0, maybe refer to an IANA AF registry? This might
>> be helpful if you want to use the same sub-TLV in OSPFv3 and
>> use the same code for parsing etc. IANA has 1 for IPv4 though.
>
> this is equivalent to section 2.1 of RFC7684. I have updated the text to
> match RFC7684.
>
>>
>> Section 5:
>> Is it intentional that the flags start in position 1 rather than
>> 0?
>
> yes. Originally we had N-flag (Node Flag) defined at position 0, but we
> moved that to the OSPFv2 Extended Prefix TLV (section 2.1 of RFC7684).
> Due to an existing implementations, we did not shift all other bits
> after that.
>
>>
>> I see that the NP flag should be ignored when M is set. Then I
>> see this text:
>>     As the Mapping Server does not specify the originator of a prefix
>>     advertisement, it is not possible to determine PHP behavior solely
>>     based on the Mapping Server advertisement.  However, PHP behavior may
>>     safely be done in following cases:
>> This seems not very precise. Could you say exactly what the behavior
>> should be, rather than saying "behavior may be done"?
>
> would changing  "may safely be done" to "SHOULD be done" be sufficient?
>
>>
>> Section 6:
>> It might be good to make clear that other flag positions are
>> reserved, set to 0 and ignored... Perhaps also point out that
>> weight is in the range 0-255
>
> fixed both.
>
>>
>> I see this sentence:
>>        If the SID/Label Sub-TLV appears in the SID/Label Binding Sub-TLV
>>        more than once, instances other than the first will be ignored and
>>
>> Should it say MUST be ignored?
>
> changed to SHOULD as the previous text says "SHOULD only appear once".
>
>>
>> Section 6.2 it says:
>>     All ERO Sub-TLVs must immediately follow the SID/Label Sub-TLV.
>>     All Backup ERO Sub-TLVs must immediately follow the last ERO Sub-TLV.
>>
>> Should these be normative MUSTs?
>
> Changed both to MUST.
> I'm also going to clarify this with Hannes, whether that is still
> required, because I do not see equivalent text in ISIS draft.
>
>>
>> In 6.2.1:
>> It would be good for all of these to specify that other flags are
>> reserved.
>
> done.
>
>
>>
>>
>> Nits:
>> The intro should perhaps mention LAN adjacency and binding SIDs?
>
> LAN Adjacency SID is a sub-type of the Adjacency SID. I have added
> sentence about binding/other SID types.
>
>>
>> 2nd paragraph of section 2 is confusing. It sounds like
>> the Opaque LSAs in 7684 were defined for SID in particular,
>> but it is a generic mechanism. Perhaps SID was the
>> motivation though?
>
> this part is a left-over from the original draft before we split to
> RFC7684 and this draft.
>
> I replaced the whole paragraph with:
>
> "Extended Prefix/Link Opaque LSAs defined in <xref target="RFC7684"/>
> are used for advertisements of the various SID types."
>
>>
>> Section 6.1:
>> It says:
>>     The ERO Metric Sub-TLV advertises the cost of an ERO path.  It is
>>     used to compare the cost of a given source/destination path.  A
>>     router SHOULD advertise the ERO Metric Sub-TLV in an advertised ERO
>>     TLV.
>>
>> Is the ERO TLV the ERO Sub-TLVs defined in 6.2? It would be good to
>> point that out.
>
> ERO Metric Sub-TLV as well as all the other ERO sub-TLVs in sectin 6.2
> are at the same level - they are all sub-TLVs of the Binding TLV. I
> added some text to 6.2 to make that clear.
>
>>
>> In 8.4.2:
>>     Broadcast, NBMA or or hybrid
>> Extra "or".
>
> fixed.
>
>>
>> Section 9:
>> There are no new registries and most of the TLVs are already
>> allocated? It seems there are a few new ones where it should
>> probably say TBD, or say something about being suggested values.
>> That was done in earlier sections. I see in some places it says
>> "are allocated" here, while it says "suggested" in the definition
>> of the TLV.
>
> section 9 lists all the updates to the four different registries. Values
> are explicitly mentioned in section 9 for every single code point.
>
>>
>> Section 10:
>> It says there are responses from 2 implementers, but I see 3.
>
> fixed
>
>>
>> Section 11:
>> Are these really all the potential security issues?
>
> I'm not aware of any others. Feel free to suggest more if required.
>
>>
>> I'm on vacation the next 2 weeks, so I may not reply to any
>> emails during that period.
>
> I will post the new version after closing on the ERO part with Hannes
> and others.
>
> thanks,
> Peter
>
>>
>> Regards,
>> Stig
>> .
>>
>